bson_append_date_time man page

bson_append_date_time() — The bson_append_date_time() function shall append a new element to a bson document containing a date and time with no timezone information. value is assumed to be in UTC format of milliseconds since the UNIX epoch. value MAY be negative.

The bson_append_date_time(3) function shall append a new element to a bson document containing a date and time with no timezone information. value is assumed to be in UTC format of milliseconds since the UNIX epoch. value